Impact of mist and acidic fog on polymer insulator samples exposed to corona discharges

Corona resulting from the metallic parts of the transmission line insulators and hardware has proven to be the potential factor in inducing the degradation of polymer insulators. Corona activity is found to increase substantially during the foul weather condition (rain, fog/mist, hoarfrost), which further promotes the ageing of polymer insulators. Present work investigates the possible corona activity under fog/moist condition and its effects on the long term performance of polymer insulators in service. The spread of corona generated plasma is observed to be different under fog condition than in normal air condition. The concentrated streamers that are originated from the corona electrode during fog condition are believed to damage the polymer shed material locally and more intensely. This was confirmed by the scanning electron microscopy and Fourier infrared spectroscopy analysis carried out on the treated polymer samples, which showed more damage on the corona treated under fog than on the samples treated under normal air condition. Further TGA and EDAX studies have shown that loss of ATH occurs on the sample due to intense corona activity.